1. Field of the Invention
The present invention relates to polymerizable compositions, polymerizates prepared from such compositions and optical articles prepared from such polymerizates. In particular, the present invention discloses a class of polymerizable compositions useful in making optical lenses which can offer superior abrasion resistance, impact resistance and/or UV protection. Moreover, the present invention discloses an apparatus and method for making optical articles using a radiation energy source capable of delivering radiations from opposite directions.
2. Background
Plastic lenses have over time become desirable for use in making optical lenses, especially of the kind useful for eyeglasses. Plastic lenses offer several advantages over glass lenses, including reduced weight and increased strength. Generally, plastic lenses for eyeware have been formed from diethylene glycol bis(allylcarbonate)(xe2x80x9cDACxe2x80x9d)(also known as xe2x80x9cCR39xe2x80x9d), which has been polymerized via free radical polymerization. DAC lenses offer relatively high impact resistence, light weight, ease of machining and polishing, and ease of dyeing. However, DAC lenses do not offer desirable abrasion resistance.
Plastic lenses can also be produced by molding of thermal plastic resins, such as polymethyl methacrylate (PMMA) and polycarbonate. However, both types of lenses have inherent drawbacks: PMMA lenses offer poor impact resistance while polycarbonate lenses offer inadequate abrasion resistance as well as solvent resistance.
One way the art has sought to improve abrasion resistance for plastic lenses includes the use of a hard coat on the surfaces of the lense through thermal curing or UV radiation curing. For example, U.S. Pat. No. 4,611,892 discloses an improved synthetic resin lens and a method for modifying the surface of the synthetic resin lens to form an inorganic film or hard coating layer securely on the surface. However, the additional hard coating process is often time consuming and has the potential to lower the overall yield of the production. Additionally, the boundary between the coating layer and the surface of the lens may cause optical defect in the resultant lens. Moreover, because currently available UV curing process utilizes a single UV light source projecting radiation energy onto a mold filled by a lens-forming material asymmetrically, the resultant lens may have surfaces with unevenly distributed hardness. The overall quality of the resultant lens may be compromised by the unevenly distributed hardness. Thus, there is a need in the art for a new curing process and apparatus that may provide more evenly distributed hardness at a reduced curing time.
The art has also looked to the polymerizable composition in producing lenses with better optical properties.
For example, U.S. Pat. No. 5,739,243 discloses polymerizable compositions of 5 to 90 weight percent of a first monomer component, which is a diacrylate of alkoxylated bisphenol A having 25 to 35 ethoxy units, and 10 to 95 weight percent of a second monomer component having at least three acrylate groups.
U.S. Pat. No. 5,556,931 discloses polymerizable compositions comprising at least two ethoxylated bisphenol A dimethacrylate type monomers, the content of which is 30 to 80 mole % having 2 to 3 ethoxy units, 20 to 50 mole % having 6 to 12 ethoxy units and less than 20 mole % having other than 2 to 30 and 6 to 12 ethoxy units.
Similarly, U.S. Pat. No. 5,583,191 discloses a transparent resin obtained by polymerizing a monomer having an alkylene oxide group, and a polyfunctional (meth) acrylate having a divalent branched hydrocarbon group.
U.S. Pat. Nos. 5,545,828 and 5,442,022 disclose polymer compositions for use in the manufacture of ophthalmic lenses composing at least 50% by weight of one to two modified bisphenol A diacrylates.
U.S. Pat. No. 5,415,816 discloses a polymerizable composition comprising bisphenol A bis(allyl carbonate) monomer and acrylate monomers.
U.S. Pat. No. 4,912,185 discloses a cross-linkable polymeric casting composition including aliphatic diacrylate (such as polyoxyalkylene glycol diacrylate) in amounts of from approximately 40% to 60% by weight, and at least one polyfunctional unsaturated cross-linking agent, such as tri or tetrafunctional acrylate, present in amounts of from approximately 10 to 30% by weight, preferably approximately 20% by weight based on the total weight of the casting composition.
In spite of the foregoing, the need still exists for a polymerizable composition that can be used to produce better optical lenses, which can offer superior abrasion resistance, impact resistance and/or UV protection.
Among other things, the present invention is based upon the surprising discovery that the use of an effective amount of at least one tetrafunctional acrylate monomer in a polymerizable composition results in optical lenses which may offer superior abrasion resistance without compromising impact resistance of the resultant lenses.
In addition, the inventors have discovered that the use of a radiation energy source capable of delivering radiations from opposite directions for curing the resins can produce better lenses with a substantially symmetrically-distributed hardness. The new curing process is time efficient and the resultant lens has an inherently integrated xe2x80x9chard-soft-hardxe2x80x9d structure which offers superior impact resistance.
In this regard, one aspect of the invention relates to a polymerizable composition comprising at least 50 percent by weight of a tetrafunctional acrylate monomer. In one embodiment of the invention, a polymerizable composition is a compound comprising of at least 50 percent by weight of a tetrafunctional acrylate monomer, from 5 to 30 percent by weight of at least one modified bisphenol A epoxy diacrylate monomer, and from 0 to 3 percent by weight of at least one UV absorber.
Also, the invention relates to a polymerizable composition comprising at least 50 percent by weight of at least one tetrafunctional acrylate monomer, from 5 to 30 percent by weight of at least one modified bisphenol A epoxy diacrylate monomer, from 0 to 25 percent by weight of at least one acrylate monomer selected from aliphatic difunctional and polyfunctional acrylates, and from 0 to 3 percent by weight of at least one UV absorber.
In another embodiment, the invention relates to a polymerizable composition comprising at least 50 percent by weight of at least one tetrafunctional acrylate monomer, from 5 to 20 percent by weight of at least one modified bisphenol A epoxy diacrylate monomer, from 0 to 25 percent by weight of at least one acrylate monomer selected from aliphatic difunctional and polyfunctional acrylates, from 0 to 3 percent by weight of at least one UV absorber, and a source of free radicals.
In addition, the invention relates to resins that are the product of polymerization of the polymerizable compositions described above and can be used as a lens-forming material.
In another aspect, the invention provides a method of preparing an optical article from a curable material containing a radiation absorber. The method includes the steps of providing a radiation energy source that has a first region delivering radiation in a first direction and a second region delivering radiation in an opposite second direction, wherein the first and second regions are arranged so as to define a space therebetween, and the space is subjected to the radiation in the first direction from the first region and the radiation in the second direction from the second region, placing the curable material in the space therebetween the first and second regions of the energy radiation source and curing the curable material to obtain the optical article by exposing the curable material to radiations from the first and second regions of the radiation energy source.
In one embodiment of the present invention, the method can be practiced to prepare an optical lens by forming a lens mold cavity having a configuration conforming to the optical lens to be molded, introducing a liquid lens-forming material into the mold cavity, wherein the liquid lens-forming material contains a UV absorber, providing a radiation energy source that has a first region delivering radiation in a first direction and a second region delivering radiation in a second, typically opposite, direction, wherein the first and second regions are arranged so as to define a space therebetween, and the space is subjected to the radiation in the first direction from the first region and the radiation in the second direction from the second region, placing the mold filled with the liquid lens-forming material in the space therebetween the first and second regions of the energy radiation source, and curing the lens-forming material within the lens mold cavity to obtain the optical lens by exposing the lens-forming material to radiations from the first and second regions of the radiation energy source.
In another embodiment of the present invention, the mold is placed substantially at the center of the space therebetween the first and second regions of the radiation energy source. Preferably, each of the first and second regions delivers UV light.
Moreover, the present invention relates to an apparatus for making an optical article. In one embodiment of the invention, the apparatus includes a mold assembly having a mold cavity. The mold assembly can have a first and second mold members to form the mold cavity for receiving a liquid curable material. The apparatus also includes a radiation energy source for curing the liquid curable material within the mold cavity to obtain the optical article. The radiation energy source includes a first region capable of delivering radiation in a first direction and a second region capable of delivering radiation in an opposite second direction. The first and second regions are arranged so as to define a space therebetween. In use, the mold assembly is located at the space therebetween the first and second regions so that the curable material is exposed to the radiations in opposite directions simultaneously from the first and second regions of the radiation energy source during curing.
In a particular embodiment of the invention, the energy radiation source includes two UV lights. The first UV light is located at the first region, and the second UV light is located at the second region. The relative distance between the two UV lights is adjustable. In another embodiment of the invention, the radiation energy source preferably includes a U-shaped UV light. The U-shaped UV light has a first arm capable of delivering UV light in a first direction and a second arm capable of delivering UV light in an opposite second direction. The mold assembly is placed between the first and second arms of the U-shaped UV light.
The apparatus and method of the present invention can be used for making optical lenses. For example, as discussed in detail below, optical lenses with better mechanical properties can be produced by using the apparatus and the method of the present invention, together with the polymerizable compositions of the present invention. It needs to be emphasized that, however, the polymerizable compositions of the present invention can be used for making optical articles using currently available apparatuses and methods. Likewise, the apparatus and method of the present invention can be used for making optical articles using currently available polymerizable compositions. Moreover, in addition to optical lenses, the present invention can be practiced in numerous applications including coatings, adhesives, medical plastics, fiber optics and glazing materials.
Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.